Actually it doesn't, which is the really cool thing about these cloaks. The cloaks are made of a metamaterial for which the refractive index is less than 1, so light travels faster than c in that medium. That's what makes them tricky (but not impossible) to build! The reduced refractive index with respect to the surrounds exactly makes up for the extra distance travelled. It's neat stuff.
How would it show movement? AFAIK the cloak should be able to move around and this movement shouldn't be visible to you.
Or do you mean they won't be able to make a flexible cloaking ninja suit that keeps cloaking the ninja as they walk, despite the suit bending? The solution to that, of course, is to roll around inside a giant hamster ball/zorb cloaking device! Watch out... i'll sneak up on you and ROLL YOU TO DEATH.
Yep, and even if you got a broadband cloak that worked at all those frequencies, you could still pick it up by a number of ways not mentioned in TFA. You could pick it up with sonar (I guess in principle it could also be an acoustic cloak to beat that too), but you could also change the refractive index of the room. The cloak is designed so that no matter what's in the cloaked region, it appears to have a refractive index of 1 (or whatever the cloak's surrounds are supposed to be). If you change the refractive index of the surrounds slightly (change temperature, spray an aerosol, fill the room with water (!)) then the cloak should be relatively easy to spot.
The other downside of these cloaks, of course, is that you can't see out of them since no light interacts with your eyes.
Yes! It got fixed in Jaunty a month or two ago - and it looked like they were sitting on the bugfix for about a month. Pretty unprofessional stuff, since many people's computers were rendered unusable, but now it's fixed and Karmic sings on my EEE. It does tell me that my battery's broken and that the SMART status of my SSD indicates that it's on its way out, but let's not shoot the messenger.
What they should have done is send the transaction details and the confirmation code in the same SMS.
Which is exactly what the Commonwealth Bank of Australia does.
Whenever you try to do anything 'serious', e.g. transfer money to someone new, change your details etc, you have to enter a code they'll send you by SMS. This SMS will briefly say what you're trying to do, e.g. a part of the account number you're sending money to. It's fast and doesn't get in your way unless you're doing something potentially dangerous
The libs and greens are voting against the filter, so yes the dentist-filter plan is dead in the water. But I wouldn't be surprised if the libs supported this copyright bill, which would be more than enough to get it through.
I never thought I'd say this, but I think I preferred Richard Alston, who had the international reputation of "Worlds Biggest Luddite", as IT minister. At least he was too incompetent to do much damage.
Oops, I neglected to mention the 'shrink' part. It's a lot easier to shrink (and warp) a submarine than make it disappear entirely. Proper cloaks have a singularity on the inner surface of the cloak, as the entire inner surface has to seem like a single point. If you build the outer part of the cloaking device properly, but just give up when you get to a certain radius, then your cloaking device more or less makes the cloaked region appear much smaller than it really is, e.g. turning your submarine-sized object into a shark-sized object. Tweak the cloak a bit and you can shape the visible object like a shark.
This kind of cloak should even be possible to build without resonant structures, since it doesn't need the presence of a medium in which the speed of sound is infinite (the singularity), it just needs a medium in which the speed of sound is greater than in water.
Actually it's the other way around - because this uses resonant cavities, it only works on a very small range of frequencies. But the 'super' thing about a superlens is that it can focus sound/light to a region smaller than any other kind of lens, 'beating the diffraction limit'.
Nup, time of flight will be exactly the same. If this is like the optics ones, then this cloak is designed so that sound is indeed bent around the object, and it's made out of a fancy resonant metamaterial that's cleverly designed so that sound travels faster through it than through the surrounding water.
You could intentionally let a little bit of light/sound in and out at your favourite frequency. Or you could choose not to be entirely invisible, designing the cloaking device to warp your submarine into, say, the shape of a shark. All the sound that would have hit the shark will be spread across your submarine's surface (or if you design the cloak REALLY cleverly it could be focussed on your receiver). So with this kind of cloak, the enemy COULD see your submarine and receiver, but it would just be disguised like a shark. Since they can see you, you can see them. And you know your cloak's design, so you can use clever computer stuff to unwarp the pictures you get of the outside world.
Not so sure. Sound reflects at an abrupt change of medium/impedance. If these acoustic cloaks are like the optical cloaks, then the innermost part of the cloaking device has an impedance of zero, which reflects all sound. So it could get noisy inside the cloak if there's no damping...
Yep, this particular design will work over a very narrow range of frequencies, because it uses resonant cavities, which are inherently narrowband. If they could build a design without the need for resonant effects, then in principle the acoustic cloak could work over a very large range of frequencies.
The idea behind the acoustic cloak is essentially the same as the optical cloaks that have already been demonstrated: 'squash' space around the object to open up a hole in the universe, as seen by light/sound sees. This uses the fact that light/sound travels faster in some materials than others - essentially a block of glass is a bit like a TARDIS, squashing space, in the sense that a ray of light circling the object from inside can 'travel further' (i.e. accumulate more phase) than a ray of light circling the object from the outside. The refractive index can be thought of as related to General Relativity's metric, i.e. a measure of how space has been 'squashed'.
So if you're clever you can warp space to create a no-go region for light, essentially choosing a point in space and opening it up to a circle. All parts of that circle have to be the same distance from each other, so light/sound has to be able to travel around that part of the circle instantly, i.e. for light the refractive index at the circle has got to be zero.
Getting a zero refractive index (or acoustic impedance - i'm not an acoustics person so i might have this wrong) is hard, and at the moment we can only do that using resonant materials (in optics, they're micro-ring resonators or fishnet structures - metamaterials). However, if you don't want to make the sub invisible, if you're happy to be able to just shrink it (or even distort it into the shape of a shark), then you don't need an impedance of zero, you just need a material in which sound travels faster than in water, the surrounding medium. The faster light travels in it, the smaller you can make your cloak.
Obviously this is an easier problem for sound than for light, since we usually want to cloak things surrounded by air, and there ain't too many natural media in which light travels faster than c.
Don't forget the upgrade from Mac OS 9 to OS X, and the massive lags when just dragging windows around the screen! OS X has been getting faster because there has been so much room for improvement.
There usually are a few touted applications of "slow light".
As a pulse/beam of light slows down, it intensifies (just like chairs on a chairlift bunch up at the slow top and bottom base stations). As the intensity of the light goes up, so do the nonlinear effects of the medium, so if you want to exploit nonlinearity, slow light is a good thing. However, this particular implementation (requiring neodymium atoms as the medium) won't be useful for this application because I don't think many people are interested in the nonlinearities of that medium
The other big application of "slow light" is relevant here - it is an optical buffer, a delay line that you can send light into. If you want to build an optical router (a challenging goal), then you need to be able to delay individual packets to avoid packet collisions. Now that slow light is supposedly sorted, you just need to get to work on the optical logic required for routing, which according to some big names, can physically never beat electronics as long as TCP/IP is still around.
Yep, WDM is useful, but if you've got two packets from two different sources coming into the switch at the same time, and they have to go into the same channel (i.e. wavelength) out of the switch because they're going to the same place, then you still need delay.
This article is claiming that metamaterials can give slow light. An optical switch needs a slow light component - where electronic switches can delay packets by temporarily storing them in memory, in an optical switch it would be easier to delay packets by slowing them down rather than stopping them outright. You'd want to delay a packet if it was about to collide with another packet. The actual routing would be done by optical logic, which is very hard and not being claimed by this research group.
Slow light can be achieved in other ways, too - e.g. photonic crystals.
Yep, but if these are just amplifiers then they amplify the noise too, so every now and then you've got to tidy up the signals and remove the noise, "regenerating" the signal. This is currently done electronically and is another bottleneck. I've just asked a colleague and all-optical regenerators are still being developed.
And I should point out that the pulses need to be delayed/buffered as part of the switching process (to avoid packet collisions) - an optical buffer using slow light will be one component in an optical switch.
Latency vs. bandwidth: ping times vs. download speeds.
The big advantage of an optical switch would not be a decrease in ping times, the advantage is that the switch has far higher bandwidth. Optical components have much faster response times than electronics, so in theory can support many more bits/sec.
All-optical regenerators (i.e. repeaters) have been developed - I'm not sure whether they've been implemented yet or whether there's a bit more work to be done (I'm not sure whether they support multiple channels yet), but it's certainly a much simpler problem that's much closer to being solved than optical switching.
Fibres can handle much more data than the electronics, so we multiplex the output of 64 electronic systems, send all that down a single fibre, demultiplex it (i.e. split it back into 64 separate fibres) and feed these signals to 64 sets of electronics. I'm pretty sure the multiplexing/demultiplexing is fast, but the problem is that you need 64 electronic routers.
Optical switching would allow much higher bandwidth per channel, meaning you can replace the 64 channels by one, and you'd only need one optical switch rather than 64 electronic ones.
Sort of. At the moment, all routing is done electronically. The electronics doesn't have as much bandwidth as the fibres feeding it due to slow response times of electronics. So whenever three or more fibres join, you have an information bottleneck. It would be wonderful if this routing could be done optically, allowing much higher bandwidth routers, removing the bottleneck.
But a router is a bit like a set of traffic lights - if two packets of information travelling to the same destination arrive the router at the same time, then one of them needs to be delayed while the other one is sent through. This requires some way of slowing pulses of light.
Today, these people are claiming that metamaterials will be useful for slowing light, and would thus be useful in such an optical router. I'm a tad skeptical about this at the moment (not sure what the losses would be), and there are several other challenges that need to be met in order to create an optical router.
nah, they sent the information about the teleported photon by.... photons. Everyone still thinks that sending information faster than light is impossible.
Don't worry, CUDOS is not funded to do science for the sake of it, it's funded to do useful things that get implemented. This particular result is just the latest record, and will be beaten before anything sees implementation, but I'm sure some of these technologies will be implemented - electronics simply can't handle 640Gbps signals on its own, these signals need to be demultiplexed by optics, and this is the best result so far.
At the moment, the alternative technology to this is laying more cables. And that's very expensive.
Slashdot Mirror
Actually it doesn't, which is the really cool thing about these cloaks. The cloaks are made of a metamaterial for which the refractive index is less than 1, so light travels faster than c in that medium. That's what makes them tricky (but not impossible) to build! The reduced refractive index with respect to the surrounds exactly makes up for the extra distance travelled. It's neat stuff.
How would it show movement? AFAIK the cloak should be able to move around and this movement shouldn't be visible to you.
Or do you mean they won't be able to make a flexible cloaking ninja suit that keeps cloaking the ninja as they walk, despite the suit bending? The solution to that, of course, is to roll around inside a giant hamster ball/zorb cloaking device! Watch out... i'll sneak up on you and ROLL YOU TO DEATH.
Yep, and even if you got a broadband cloak that worked at all those frequencies, you could still pick it up by a number of ways not mentioned in TFA. You could pick it up with sonar (I guess in principle it could also be an acoustic cloak to beat that too), but you could also change the refractive index of the room. The cloak is designed so that no matter what's in the cloaked region, it appears to have a refractive index of 1 (or whatever the cloak's surrounds are supposed to be). If you change the refractive index of the surrounds slightly (change temperature, spray an aerosol, fill the room with water (!)) then the cloak should be relatively easy to spot.
The other downside of these cloaks, of course, is that you can't see out of them since no light interacts with your eyes.
And murdoch's news.com.au's robots.txt file even directs bots to the sitemap!
/*comments/* /*print/* /*email/* /*SIT* /*.swf /printpage/
User-agent: *
Disallow:
Disallow:
Disallow:
Disallow:
Disallow:
Disallow:
Disallow: */404*
Sitemap: http://www.news.com.au/sitemap.xml
Sitemap: http://www.news.com.au/adelaidenow-sitemap.xml
Sitemap: http://www.news.com.au/couriermail-sitemap.xml
Sitemap: http://www.news.com.au/dailytelegraph-sitemap.xml
Sitemap: http://www.news.com.au/heraldsun-sitemap.xml
Sitemap: http://www.news.com.au/perthnow-sitemap.xml
Yes! It got fixed in Jaunty a month or two ago - and it looked like they were sitting on the bugfix for about a month. Pretty unprofessional stuff, since many people's computers were rendered unusable, but now it's fixed and Karmic sings on my EEE. It does tell me that my battery's broken and that the SMART status of my SSD indicates that it's on its way out, but let's not shoot the messenger.
What they should have done is send the transaction details and the confirmation code in the same SMS.
Which is exactly what the Commonwealth Bank of Australia does.
Whenever you try to do anything 'serious', e.g. transfer money to someone new, change your details etc, you have to enter a code they'll send you by SMS. This SMS will briefly say what you're trying to do, e.g. a part of the account number you're sending money to. It's fast and doesn't get in your way unless you're doing something potentially dangerous
The libs and greens are voting against the filter, so yes the dentist-filter plan is dead in the water. But I wouldn't be surprised if the libs supported this copyright bill, which would be more than enough to get it through.
I never thought I'd say this, but I think I preferred Richard Alston, who had the international reputation of "Worlds Biggest Luddite", as IT minister. At least he was too incompetent to do much damage.
Oops, I neglected to mention the 'shrink' part. It's a lot easier to shrink (and warp) a submarine than make it disappear entirely. Proper cloaks have a singularity on the inner surface of the cloak, as the entire inner surface has to seem like a single point. If you build the outer part of the cloaking device properly, but just give up when you get to a certain radius, then your cloaking device more or less makes the cloaked region appear much smaller than it really is, e.g. turning your submarine-sized object into a shark-sized object. Tweak the cloak a bit and you can shape the visible object like a shark.
This kind of cloak should even be possible to build without resonant structures, since it doesn't need the presence of a medium in which the speed of sound is infinite (the singularity), it just needs a medium in which the speed of sound is greater than in water.
Actually it's the other way around - because this uses resonant cavities, it only works on a very small range of frequencies. But the 'super' thing about a superlens is that it can focus sound/light to a region smaller than any other kind of lens, 'beating the diffraction limit'.
Nup, time of flight will be exactly the same. If this is like the optics ones, then this cloak is designed so that sound is indeed bent around the object, and it's made out of a fancy resonant metamaterial that's cleverly designed so that sound travels faster through it than through the surrounding water.
You could intentionally let a little bit of light/sound in and out at your favourite frequency. Or you could choose not to be entirely invisible, designing the cloaking device to warp your submarine into, say, the shape of a shark. All the sound that would have hit the shark will be spread across your submarine's surface (or if you design the cloak REALLY cleverly it could be focussed on your receiver). So with this kind of cloak, the enemy COULD see your submarine and receiver, but it would just be disguised like a shark. Since they can see you, you can see them. And you know your cloak's design, so you can use clever computer stuff to unwarp the pictures you get of the outside world.
Not so sure. Sound reflects at an abrupt change of medium/impedance. If these acoustic cloaks are like the optical cloaks, then the innermost part of the cloaking device has an impedance of zero, which reflects all sound. So it could get noisy inside the cloak if there's no damping...
Yep, this particular design will work over a very narrow range of frequencies, because it uses resonant cavities, which are inherently narrowband. If they could build a design without the need for resonant effects, then in principle the acoustic cloak could work over a very large range of frequencies.
The idea behind the acoustic cloak is essentially the same as the optical cloaks that have already been demonstrated: 'squash' space around the object to open up a hole in the universe, as seen by light/sound sees. This uses the fact that light/sound travels faster in some materials than others - essentially a block of glass is a bit like a TARDIS, squashing space, in the sense that a ray of light circling the object from inside can 'travel further' (i.e. accumulate more phase) than a ray of light circling the object from the outside. The refractive index can be thought of as related to General Relativity's metric, i.e. a measure of how space has been 'squashed'.
So if you're clever you can warp space to create a no-go region for light, essentially choosing a point in space and opening it up to a circle. All parts of that circle have to be the same distance from each other, so light/sound has to be able to travel around that part of the circle instantly, i.e. for light the refractive index at the circle has got to be zero.
Getting a zero refractive index (or acoustic impedance - i'm not an acoustics person so i might have this wrong) is hard, and at the moment we can only do that using resonant materials (in optics, they're micro-ring resonators or fishnet structures - metamaterials). However, if you don't want to make the sub invisible, if you're happy to be able to just shrink it (or even distort it into the shape of a shark), then you don't need an impedance of zero, you just need a material in which sound travels faster than in water, the surrounding medium. The faster light travels in it, the smaller you can make your cloak.
Obviously this is an easier problem for sound than for light, since we usually want to cloak things surrounded by air, and there ain't too many natural media in which light travels faster than c.
Don't forget the upgrade from Mac OS 9 to OS X, and the massive lags when just dragging windows around the screen! OS X has been getting faster because there has been so much room for improvement.
There usually are a few touted applications of "slow light".
As a pulse/beam of light slows down, it intensifies (just like chairs on a chairlift bunch up at the slow top and bottom base stations). As the intensity of the light goes up, so do the nonlinear effects of the medium, so if you want to exploit nonlinearity, slow light is a good thing. However, this particular implementation (requiring neodymium atoms as the medium) won't be useful for this application because I don't think many people are interested in the nonlinearities of that medium
The other big application of "slow light" is relevant here - it is an optical buffer, a delay line that you can send light into. If you want to build an optical router (a challenging goal), then you need to be able to delay individual packets to avoid packet collisions. Now that slow light is supposedly sorted, you just need to get to work on the optical logic required for routing, which according to some big names, can physically never beat electronics as long as TCP/IP is still around.
Actually several years ago a group slowed light down to 17m/s, slower than a bicycle. But that was a very different technology to metamaterials.
Yep, WDM is useful, but if you've got two packets from two different sources coming into the switch at the same time, and they have to go into the same channel (i.e. wavelength) out of the switch because they're going to the same place, then you still need delay.
This article is claiming that metamaterials can give slow light. An optical switch needs a slow light component - where electronic switches can delay packets by temporarily storing them in memory, in an optical switch it would be easier to delay packets by slowing them down rather than stopping them outright. You'd want to delay a packet if it was about to collide with another packet. The actual routing would be done by optical logic, which is very hard and not being claimed by this research group.
Slow light can be achieved in other ways, too - e.g. photonic crystals.
Yep, but if these are just amplifiers then they amplify the noise too, so every now and then you've got to tidy up the signals and remove the noise, "regenerating" the signal. This is currently done electronically and is another bottleneck. I've just asked a colleague and all-optical regenerators are still being developed.
And I should point out that the pulses need to be delayed/buffered as part of the switching process (to avoid packet collisions) - an optical buffer using slow light will be one component in an optical switch.
Latency vs. bandwidth: ping times vs. download speeds.
The big advantage of an optical switch would not be a decrease in ping times, the advantage is that the switch has far higher bandwidth. Optical components have much faster response times than electronics, so in theory can support many more bits/sec.
All-optical regenerators (i.e. repeaters) have been developed - I'm not sure whether they've been implemented yet or whether there's a bit more work to be done (I'm not sure whether they support multiple channels yet), but it's certainly a much simpler problem that's much closer to being solved than optical switching.
Fibres can handle much more data than the electronics, so we multiplex the output of 64 electronic systems, send all that down a single fibre, demultiplex it (i.e. split it back into 64 separate fibres) and feed these signals to 64 sets of electronics. I'm pretty sure the multiplexing/demultiplexing is fast, but the problem is that you need 64 electronic routers.
Optical switching would allow much higher bandwidth per channel, meaning you can replace the 64 channels by one, and you'd only need one optical switch rather than 64 electronic ones.
Sort of. At the moment, all routing is done electronically. The electronics doesn't have as much bandwidth as the fibres feeding it due to slow response times of electronics. So whenever three or more fibres join, you have an information bottleneck. It would be wonderful if this routing could be done optically, allowing much higher bandwidth routers, removing the bottleneck.
But a router is a bit like a set of traffic lights - if two packets of information travelling to the same destination arrive the router at the same time, then one of them needs to be delayed while the other one is sent through. This requires some way of slowing pulses of light.
Today, these people are claiming that metamaterials will be useful for slowing light, and would thus be useful in such an optical router. I'm a tad skeptical about this at the moment (not sure what the losses would be), and there are several other challenges that need to be met in order to create an optical router.
nah, they sent the information about the teleported photon by.... photons. Everyone still thinks that sending information faster than light is impossible.
Don't worry, CUDOS is not funded to do science for the sake of it, it's funded to do useful things that get implemented. This particular result is just the latest record, and will be beaten before anything sees implementation, but I'm sure some of these technologies will be implemented - electronics simply can't handle 640Gbps signals on its own, these signals need to be demultiplexed by optics, and this is the best result so far.
At the moment, the alternative technology to this is laying more cables. And that's very expensive.